Stoneacre Motor Group in Worksop

I've been waiting for approval of a repair under warrantee by Stoneacre Worksop / Doncaster (bonnet rusting on the underside) for a 2 year old Fiat Panda since August 15. I've contacted them in person / by email / phone easily over 15 times. I've reported concerns to head office, made a formal complaint and still no progress. Of all the times I've contacted them I've only had the promised reply 1 single time, by a receptionist. Its well over 100 days and they still haven't approved it, yet alone fixed it - Utterly pathetic in my view.